Rate of increase reveals much more about a population than the speed with which it grows. It measures a population’s general well-being, describing the average reaction of all members of the population to the collective action of all environmental influences. No other statistic summarizes so concisely the demographic vigour of a population.

G. Caughley

Population Ecology: The Basics

• How do births, deaths, immigration, & emigration affect wildlife populations?

• What affects births, deaths, immigration, & emigration?

• What are demographic characteristics?

• What is the difference between exponential & logistic population growth?

Population Ecology: The Basics

• What is Aldo’s model?

• What is carrying capacity?

• What are patterns of abundance and what controls them?

• What is metapopulation and how does it relate to wildlife population dynamics?

• Who cares?

Population Ecology: The Basics

• What is a population?

• Why not deal with individuals?

(U.S Fish & Wildlife Service) (U.S Fish & Wildlife Service)

Population Ecology: The Basics

• N = B + I – D – E (demographic characteristics)

• Nt+1 = Nt + Bt + It – Dt – Et

N

Effects of: Harvest Restocking Habitat Weather Other organisms

Population SizeBirths

Deaths

Immigration

Emigration

♂:♀

Juvenile:Adult

Population Ecology: The Basics

• Population growth without resource limitation– Exponential

• Nt = N0ert • dN/dt = N/t = rN

– Assumes no I & E or I = E– Assumes no structure

– r» Instantaneous rate of increase,

intrinsic rate of increase, Malthusian parameter, or per capita rate of increase

» b - d» Units: ind/(ind*time)» Based on 0

N

Time

A B

N

dN/d

t

A B

Biotic Potential

C

Population Ecology: The Basics• Population growth with resource limitation (in relation to conditions)

– Logistic growth• Nt = K/(1 + [{K - N0}/N0]e-rt)• dN/dt = rN(1 - [N/K])

– Assumes no I & E or I = E– Assumes no structure

– K = carrying capacity» Max. # the environment can support» Assumes constant K» Can change with time & space» K = N?» K > N?» K < N?» K = ∞?

– Density-dependence N

dN/d

tN

Time

Accelerating Phase

K

Inflection Point (½ K)

DeceleratingPhase

Inflection Point (½ K)

K

Population Ecology: The Basics

• Population growth with resource limitation (in relation to conditions)

– Logistic growth• Nt = K/(1 + [{K - N0}/N0]e-rt)• dN/dt = rN(1 - [N/K])

– r v. dN/dt

– Unused portion of carrying capacity» (1 - [N/K])

» N = 2, K = 100 → 0.98» N = 98, K = 100 → 0.02

N

dN/d

tN

Time

Accelerating Phase

K

Inflection Point (½ K)

DeceleratingPhase

Inflection Point (½ K)

K

Population Ecology: The Basics

• What is this thing called Carrying Capacity?

– Ecologically-based • K-carrying capacity (KCC)

– Socio-economically-based• I-carrying capacity (ICC)• Optimum carrying capacity (OCC)• Minimum-impact carrying capacity (MCC)

– Animals must be removed

N

Time

MCC

KCC

ICC (½ K) OCC

Population Ecology: The Basics• Aldo Leopold’s Population Model

– Decimating factors– Welfare factors

– Other possibilities?• Exposure• Space• Harvest = removal

– The limiting factor (link)?

– Influences• Land-uses• Weather• Fire

N

Time

K

Inflection Point (½ K)

Hunting (Harvest)

Diseases & Parasites

Accidents

Starvation

FoodCoverW

ater

Special Factors

WelfareFactors

Predation

Env

ironm

enta

l Res

ista

nce

DecimatingFactors

Biotic Potential

Population Ecology: The Basics

• Other patterns of abundance– Density-dependent v. density-independent factors– Causes?

N

Time

N

Time

N

Time

D

BA

N

Time

C

KK

K

Population Ecology: The Basics

• Metapopulations– Groups of local populations

• Subpopulations or demes• Size, quality, connectivity, & distance (I & E are important)

– Island Biogeography & Conservation Biology» Matrix

Population Ecology: The Basics

• Minimum viable populations (MVP)– National Forest Management Act of 1976

– Species- & site-specific

– 50/500 rule

USDA photo by: Bob Nichols

Population Ecology: The Basics• Minimum viable populations (MVP)

– Shaffer (1981)• Need for performance criteria

• 99% chance of surviving for 1000 years despite stochastic events

– Genetic stochasticity– Environmental stochasticity– Natural catastrophes– Demographic stochasticity

» BBDBBD v. DDBBBB

– Importance of individuals• Florida panther

(U.S Fish & Wildlife Service)

Population Ecology: The Basics

• Effects of sex & age structure on population growth?

Population SizeBirths

Deaths

Immigration

Emigration

♂:♀

Juvenile:Adult

Population Ecology: The Basics

• So what!